A comprehensive analysis of tidal notches in the Mediterranean Sea

Recent works (Evelpidou et al., 2012) suggest that the modern tidal notch is disappearing worldwide due sea level rise over the last century. In order to assess this hypothesis, we measured modern tidal notches in several of sites along the Mediterranean coasts. We report observations on tidal notches cut along carbonate coasts from 73 sites from Italy, France, Croatia, Montenegro, Greece, Malta and Spain, plus additional observations carried outside the Mediterranean. At each site, we measured notch width and depth, and we described the characteristics of the biological rim at the base of the notch. We correlated these parameters with wave energy, tide gauge datasets and rock lithology.

Our results suggest that, considering 'the development of tidal notches the consequence of midlittoral bioerosion' (as done in Evelpidou et al., 2012) is a simplification that can lead to misleading results, such as stating that notches are disappearing. Important roles in notch formation can be also played by wave action, rate of karst dissolution, salt weathering and wetting and drying cycles. Of course notch formation can be augmented and favoured also by bioerosion which can, in particular cases, be the main process of notch formation and development.

Our dataset shows that notches are carved by an ensemble rather than by a single process, both today and in the past, and that it is difficult, if not impossible, to disentangle them and establish which one is prevailing. We therefore show that tidal notches are still forming, challenging the hypothesis that sea level rise has drowned them.

近期研究（Evelpidou等人，2012）指出，近一个世纪以来，全球范围内的现代潮蚀龛（tidal notch）正因海平面上升而逐渐消失。为验证该假说，我们沿地中海沿岸多个点位开展了现代潮蚀龛的测量工作。本研究报道了来自意大利、法国、克罗地亚、黑山、希腊、马耳他及西班牙的73处碳酸盐海岸潮蚀龛的观测数据，同时补充了地中海以外区域的相关观测结果。在每一处点位，我们均测量了潮蚀龛的宽度与深度，并描述了龛底生物缘的特征；同时将这些参数与波浪能、潮位站数据集及岩石岩性进行了相关性分析。

本研究结果表明，将"潮蚀龛的发育仅归因于潮间带生物侵蚀作用"（如Evelpidou等人2012年的研究）是一种过于简化的认知，该认知可能会得出误导性结论，例如断言潮蚀龛正在消失。波浪作用、岩溶溶蚀速率、盐风化以及干湿循环等过程，同样对潮蚀龛的形成发挥着重要作用。当然，生物侵蚀作用也可促进潮蚀龛的发育，在特定场景下甚至可成为潮蚀龛形成与演化的主导过程。

本数据集表明，无论在现今还是过去，潮蚀龛均是多种过程共同作用的产物，而非单一过程塑造而成；即便并非完全不可能，也很难将这些过程完全区分并确定其中哪一种占主导地位。由此可见，潮蚀龛至今仍在形成，这对"海平面上升已将其淹没"的假说构成了挑战。